Of all the shopworn, will-not-fly, don’t-even-think-of-trotting-it-out excuses for cheating on your significant other, the “I couldn’t help it” ploy has got to be the worst.

You can’t help sneezing; you can’t help a hiccup. Skulking around, hiding receipts, erasing text messages and all the sundry other tasks that precede any decent assignation take a wee bit more conscious planning. And yet, according to a new study, it may be fair to say that while you jolly well could help cheating, your particular genes did make things more difficult. (More on Time.com:5 Little-Known Truths About American Sex Lives)

Infidelity — and, for that matter, any act of fleeting, uncommitted sex — always has an element of risk about it. There’s the possibility of getting caught, there’s the possibility of catching something, there’s the possibility that the charmer in the bar will turn creepy in the boudoir. (Eliot Spitzer, we’re looking at your socks.) And while those risks are enough to keep most people on the straight, narrow and relatively chaste, for some folks danger has the opposite effect. It’s the very fact that things are dangerous that is the source of most of the thrills. If that weren’t the case do you think there would be any roller coasters, bungee jumpers or poisonous blowfish eaters?

Justin Garcia, a doctoral fellow in evolutionary biology and health at Binghamton University in New York, wanted to determine just what might distinguish people who are thrilled by sexual risk from people who recoil from it, and he already knew one place to look: the DRD4 gene, which helps regulate dopamine receptors. Dopamine is one of the brain’s most versatile neurotransmitters, playing a role in a host of phenomena, including motivation, reward and sexual gratification. Scientists already knew that the DRD4 gene is involved in thrill-seeking behaviors such as gambling and drinking, and Garcia suspected it might play a role in high-wire sex too. (More on Time.com: Study of American Sex Habits Suggests Boomers Need Sex Ed)

Assembling a sample group of 181 young men and women, he and his colleagues took detailed sexual histories, including information about the volunteers’ number of sexual partners and how well they knew the people they bedded before the intimacies began. They also collected DNA samples. When Garcia compared the subjects’ DRD4 profile with their sexual histories, he found that the DNA and the dalliances indeed lined up.

“What we found was that individuals with a certain variant of the DRD4 gene were more likely to have a history of uncommitted sex, including one-night stands and infidelity,” he said. “The motivation seems to come from a system of pleasure and reward, which is where the release of dopamine comes in.” Garcia explains that the three big emotional elements of a dopamine rush are high risk, substantial rewards and variable motivation — or numerous ways the experience can pay off. All three x-factors are manifestly at play during a sexual romp.

In one respect, Garcia’s findings match another argument straying partners often make when caught in flagrante — that the affair does not necessarily say anything about the commitment the betrayer feels to the prime relationship. The heart, the head and other relevant organs all respond to different motivations, and the DRD4 appeals to the least reasoning, most impulsive of them. (More on Time.com: Can an iPhone App Save Your Marriage?)

Still, Garcia insists, “the study doesn’t let transgressors off the hook. These relationships are associative, which means not everyone with this genotype will have one-night stands or commit infidelity. [The] genes do not give anyone an excuse, but they do provide a window into how our biology shapes our propensities for a wide variety of behaviors.”

That, of course, is quite a mouthful for a faithless partner to argue when an affair is exposed — sound science though it may be. Better to go with “I’m really, really sorry” and hope for the best.